1. Field of the Invention
This invention relates to a novel inorganic filler which can be highly loaded in resin compositions, typically epoxy resin compositions without increasing viscosity, thus providing resin compositions having a low melt viscosity enough to mold. It also relates to an epoxy resin composition loaded with the inorganic filler and a semiconductor device encapsulated with a cured product of the composition.
2. Prior Art
Prior art epoxy resin compositions used for the encapsulation of semiconductor devices generally contain less than 80% by weight of an inorganic filler. To improve the reflow soldering resistance, it becomes a recent mainstream technique that a low viscosity resin is as a main component and a large amount of an inorganic filler is blended in the resin to reduce a percent water absorption. When such highly loaded resin compositions having a very low content of the resin component are produced by conventional well-known continuous kneaders, the resulting compositions have a high viscosity and poor moldability because the wetting of the filler with the resin is insufficient.
In this regard, we found that a substantial drop of moldability occurs when the inorganic filler used contains a large proportion of a filler component having a specific surface area in excess of 10 m.sup.2 /g and a particle size of less than 2 .mu.m, especially less than 0.5 .mu.m. Also, when a filler is produced by a conventional method, the content of submicron particles (having a particle size of less than 1 .mu.m) somewhat varies between lots. Then moldability depends on a particular lot of filler. Such inconvenient problems can be overcome by redesigning the screw of the continuous kneader or extending the kneading time. Unfortunately, these approaches are low in productivity and add to the cost.
It is thus desired to overcome the problems associated with high loadings of inorganic filler.